The overall objective of the proposed studies is to gain an understanding of the interrelationships between DNA repair, damage tolerance, and damage prevention pathways in the eukaryotic cellular response to DNA damage caused by two important classes of genotoxic agents. The goal of the first Specific Aim is to dissect the relationships between the DNA excision repair and DNA damage tolerance pathways in response to DNA damage in the nucleus in yeast. This will be accomplished through the utilization of a battery of mutant strains in a series of genetic and molecular biological experimental strategies designed to probe known, underlying pathway connections affecting the cytotoxic, mutagenic and recombinogenic effects of environmental and endogenous oxidative. The goal of the second specific aim will be to dissect such relationships in response to DNA damage in the mitochondria with an emphasis on a set of proteins we have recently identified as functioning in mtDNA damage resistance. The goal of the third specific aim is to identify and begin characterization of additional, key components of the interconnected damage resistance pathways through the utilization of gene microarray and biochemical approaches. It is anticipated that these studies will reveal important relationships and communication circuitries that exist for responding to genotoxic stress agents and should provide insights into the mechanisms that maintain or disrupt genetic stability during the course of such responses in eukaryotes, including humans. The success of these studies (particularly Specific Aim 2) will depend heavily on the investigators synergistic collaboration with Project 1 as well as maintaining their previously established ties with the other groups in this Program Project.